If you are not divorced yet, it is illegal (in my state anyway) to drop health insurance before the final divorce is signed. Going to have to file in court, see if you they will allow you to file emergency hearing or if you have a court date coming up make that priority to be dealt with. If you have lawyer, they may be able to send her a strong letter to add you back on or she will be responsible for medical bills.
At same time, see if you qualify for state health benefits (they can be back dated to cover last dr appt). If you can get health through your job, add it (qualifying event will be you lost insurance). You were going to have to get insurance eventually although what she did was wrong and might have been against the law. Depending on how far into the divorce process you are, might not be worth it to file in court but use it against her in the proceedings.